As a conventional air-conditioning system uses a main branch unit and a plurality of sub-branch units serially connected to the main branch unit to supply a heat medium to indoor units in a multi-air-conditioning apparatus in which the indoor units are connected to one outdoor unit.
In this air-conditioning system, the main branch unit is connected to the sub-branch units by three refrigerant pipes in order to freely select a cooling operation and a heating operation in each of the indoor units, and each of the sub-branch units generates cooling energy and heating energy and supplies the cooling energy and the heating energy to the indoor units (see Patent Literatures 1 and 2).